As part of utilization of biomass energy, attempts are made to obtain ethanol by decomposition of cellulose or hemicellulose which is a principal component of plants. In such attempts, they are planning to use the obtained ethanol for fuel by partly mixing it mainly in automotive fuel or by using it as an alternative fuel for gasoline.
Principal components of plants include cellulose (polymer of glucose which is C6 monosaccharide composed of six carbons), hemicellulose (polymer of C5 monosaccharide composed of five carbons and C6 monosaccharide), lignin, and starch. Ethanol is generated by fermentation action of microorganisms such as yeast from saccharides such as C5 saccharides including C5 monosaccharide, C6 saccharides including C6 monosaccharide and oligosaccharides which are complexes thereof as a source material.
For decomposition of cellulosic biomass such as cellulose or hemicellulose, the following three methods are planned to be industrially applied: 1) method of hydrolyzing by means of the oxidizing power of strong acid such as sulfuric acid, 2) method of enzymatically decomposing, and 3) method of utilizing the oxidizing power of supercritical water or subcritical water. However, in the acid decomposition method of 1) the added acid is an inhibitory substance for fermentation of yeast, and hence it is necessary to conduct a treatment of neutralizing the added acid before alcohol fermentation of saccharides after decomposition of cellulose or hemicellulose into saccharides, and this leads to difficulty in practical application for the economical reason in terms of the treatment cost. The enzymatic decomposition method 2) allows a treatment at a normal temperature and a constant pressure, however, an effective enzyme has not been found, and even if an effective enzyme is found, the production cost of the enzyme is probably high, and the prospects for industrial scale realization are still far from certain in the economical aspect.
As the method of hydrolyzing cellulosic biomass by supercritical water or subcritical water to produce saccharides of 3), Patent document 1 discloses a production method of saccharides capable of separating between saccharides containing C5 monosaccharide and C6 monosaccharide and saccharides containing C6 monosaccharide and recovering them, in addition to obtaining saccharides from wood biomass with high yield and high efficiency. The production method of saccharides of Patent document 1 includes: a first slurry heating step (S1) of heating a slurry prepared by adding high-temperature and high-pressure water to wood biomass; a first separating step (S2) of separating the heated slurry into a liquid ingredient and a solid ingredient a second slurry heating step (S3) of adding water to the separated solid ingredient to render it a slurry, and heating the slurry; a second separating step (S4) of separating the heated slurry into a liquid ingredient and a solid ingredient; and a useful ingredient achieving step (S5) of removing water from the separated liquid ingredient to achieve saccharides; and is characterized by further achieving saccharides by removing water from the liquid ingredient separated in the first separating step (S2) in addition to achieving saccharides in the useful ingredient achieving step (S5).
Patent document 2 discloses a method of hydrolyzing biomass that hydrolyzes biomass by the use of pressurized hot water, comprising: a first step of hydrolyzing mainly hemicellulose in the biomass; and a second step of hydrolyzing mainly cellulose in a residue obtained in the first step, wherein a liquid used in the first step includes a filtrate obtained by solid-liquid separation conducted after end of the second step. Patent document 2 also discloses to use, as a liquid for use in the hydrolysis of the first step, part of water that is recovered after washing a residue obtained by solid-liquid separation after end of the first step with water, together with the filtrate obtained by solid-liquid separation after end of the second step, and to use the remainder of the slurry in the second step.
On the other hand, as a device for conducting a dehydration treatment of an object to be dehydrated in the form of a slurry or a sludge, a belt type dehydrating device is known. For example, Patent Literature 3 discloses, as a filter cloth belt type dehydrating device capable of efficiently conducting a washing treatment of removing chlorine content from an object to be dehydrated with a simple structure, a filter cloth belt type dehydrating device having a filter cloth belt that is able to filter an object to be treated in the form of a slurry or a sludge and is wounded around in a endless manner and circled, wherein multiple stages of negative pressure dehydrating units each dehydrating the object to be dehydrated by action of suction negative pressure from the side of the bottom face of the filter cloth belt are disposed along the circling direction of the filter cloth belt, and a washing water overflow weir is provided above or above on the upstream side of at least one negative pressure dehydrating unit among the negative pressure dehydrating units of the second or later stage from the upstream side of the circling direction of the filter cloth belt, and curtain-like washing water flowing out from the washing water overflow weir is fed so that it reaches the full width of the object to be dehydrated on the filter cloth belt while the filter belt is continuously circled.